Patent Document 1 (JP S59-201965 A) and Patent Document 2 (JP H11-200975 A) disclose a fuel supply device in which multiple fuel filters are disposed in series in a fuel passage. These configurations are advantageous to set a filtration capacity that is an amount of fuel that the fuel supply device is capable of filtering.
Patent Document 3 (JP 2009-257103 A) discloses a fuel-filter abnormality detection device that determines whether a fuel filter is clogged based on a fuel pressure.
As disclosed in Patent Documents 1 and 2, efforts have been made to set a predetermined filtration performance for protection of an internal combustion engine. On the other hand, in actual use, an engine may be operated without a fuel filter for various reason such as cost saving or unavailability of a replacement filter. Alternatively, a non-authentic product lower in filtration performance may be used. In these cases, a desired filtration performance cannot be obtained. In addition, in such usage environments, a low-quality fuel containing relatively-numerous foreign objects may be used. Thus, it may be difficult to protect the engine.
The fuel-filter abnormality detection device of Patent Document 3 detects filter clogging that is one of abnormalities of the fuel filter. However, as described above, when the fuel filter is not used, or when a low-quality fuel filter is used, a fuel pressure corresponding to the filter clogging is not detected. Thus, the abnormality of the fuel filter cannot be detected in usage without a fuel filter or usage with a low-quality fuel filter having a low filtration performance.